This invention relates generally to nuclear reactors and, more particularly, to assemblies and methods for reinforcing piping for coolant spray within reactor pressure vessel of such reactor.
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A core shroud typically surrounds the core and is supported by a shroud support structure.
Boiling water reactors generally include piping for core spray cooling water. Core spray piping is used to deliver water from outside the RPV to core spray spargers inside the RPV. The core spray piping and spargers deliver coolant water to the reactor core.
The core spray cooling water is typically supplied to the reactor core region through a sparger T-box which penetrates the shroud wall. The distal end of the sparger T-box is internal to the shroud and is capped by a flat cover plate welded to the distal end of the sparger T-box. A piping tee is formed by the welded union of the sparger T-box, sparger T-box cover plate, and two sparger pipes.
The welded unions between the T-box, cover plate and sparger pipes are susceptible to cracking. There is a risk that the cracks in these welds may propagate by progressing circumferentially around the welded joint. If circumferential cracking occurs in the welded unions, unpredictable cooling water leakage may result.
Intergranular stress corrosion cracking (IGSCC) occurs in reactor components exposed to high temperature water, such as structural members, piping, fasteners, and welds. The reactor components are subject to a variety of stresses associated with differences in thermal expansion, the operating pressure needed for the containment of the reactor cooling water, and other stress sources such as residual stresses from welding, cold working and other inhomogeneous metal treatments. Water chemistry, welding, heat treatment and radiation can increase the susceptibility of metal in a component to IGSCC.
There is a long felt need for a method and means to reinforce welded joints. Reinforcement helps prevent separation of the welded piping joints. It would be desirable to provide a clamping system to provide structural integrity to the sparger T-box and hold the welded joints together in the event of weld failure.